4-5% of people with lupus have negative test results, and a larger number, as much as 40% of people with RA have neg blood tests for it. Both lupus and RA can cause a cough. Since this started with muscle pain, I would also ask to have your CK levels checked on your blood, which is elevated in myositis (muscle inflammation). Since your sed rate is high, there is definitely something going on, and the rheum will run more tests to try to pin it down. Some people develop symptoms of autoimmune diseases before their labs show anything definitive, so it can take awhile to get a diagnosis. I hope the rheum has some answers for you and starts you on some treatment to help ease your pain.